A review on chitosan-based membranes for sustainable CO2 separation applications: Mechanism, issues, and the way forward

Effective carbon dioxide (CO₂) separation by nominal energy utilization is the factual attempt in the present era of energy scarcity and environmental calamity. In this perspective, the membrane- based gas separation technology is a budding endeavour owing to its cost -effectiveness, ease of operational maintenance and compact modular design. Among various membrane materials, bio-based polymers are of interest as they are abundant and can be obtained from renewable resources, and can also reduce our dependency on exhaustible fossil fuel-based sources. In this review, the structure-property relationship of chitosan and some of its film-forming derivatives has been critically studied for the first time in view of the fundamental properties required for gas separation applications. Various factors affecting the gas permeation performance of chitosan-based membranes have been highlighted along with prospects and propositions for the design of a few novel bio-based membranes based on the exhaustive analyses.

Hyperthin Membranes for Gas Separations via Layer-by-Layer Assembly

Thin film formation via the Layer-by-Layer method is now a well-established and broadly used method in materials science. We have been keenly interested in exploiting this technique in the area of gas separations. Specifically, we have sought to create hyperthin (<100 nm) polyelectrolyte-based membranes that have practical potential for the separation of CO₂ from N₂ (flue gas) and H₂ from CO₂ (syngas). In this personal account, we summarize recent studies that have been aimed at measuring the influence of a variety of factors that can affect the permeability and permeation selectivity of hyperthin polyelectrolyte multilayers (PEMs).

Improving the Transport and Antifouling Properties of Poly(vinyl chloride) Hollow-Fiber Ultrafiltration Membranes by Incorporating Silica Nanoparticles

Poly(vinyl chloride) (PVC)/SiO₂ nanocomposite hollow-fiber membranes with different nano-SiO₂ particle loadings (0-5 wt %) were fabricated using the dry-jet wet-spinning technique. Effects of SiO₂ nanoparticles on the morphology of the prepared hollow-fiber membranes were investigated using scanning electron microscopy. Transport and antifouling properties of the fabricated membranes were evaluated by conducting pure-water permeation, solute rejection, and fouling resistance experiments. These studies indicated that incorporating silica nanoparticles into the PVC matrix during phase inversion lowers the hydraulic resistance through the membrane and narrows the selective membrane pores. Moreover, the nanocomposite membranes showed better antifouling properties compared to the pristine membrane during the ultrafiltration of a milk solution because of improved hydrophilicity and uniform dispersion of the nanoparticles. This work indicates that embedding silica nanoparticles into the PVC matrix is a promising method for producing cost-effective hollow-fiber ultrafiltration membranes with superior transport and antifouling properties.

Graphene-Incorporated Biopolymeric Mixed-Matrix Membrane for Enhanced CO2 Separation by Regulating the Support Pore Filling

The CO₂ separation performance by a membrane is influenced essentially by film thickness, temperature, moisture, and pressure. Pore formation on the active layer and pore clogging of the membrane support are critical factors that impedes the CO₂ separation performance. This study involves the development of a novel nanocomposite membrane (CS/SF/GNP) consisting of chitosan (CS), silk fibroin (SF), and graphene nanoparticles (GNP). The CS acts as the matrix, SF contributes to the CO₂ facilitated transport by its inherent amines as carriers, and GNP helped in counteracting the support pore blockage during the gas separation test. The positive effect of GNP in the CS/SF/GNP was further apparent in the CO₂ permeance inconsequential drop of ∼7% during the initial 12 h in the presence of moisture and pressure. The detailed characterizations including FESEM, AFM, and swelling were performed for the membranes. The effect of sweep water flow rate, temperature, and feed absolute pressure on CO₂ separation performance from binary gas were performed. The CS/SF/GNP membrane exhibited CO₂ permeance of 159 GPU and CO₂/N₂ selectivity of 93 at 90 °C and a feed absolute pressure of 2 bar having a sweep side water flow rate of 0.05 mL/min. Further, when CS/SF/GNP membrane was tested to separate CO₂ from ternary gas mixture (CO₂/N₂/H₂), it displayed excellent CO₂ permeance of 126 GPU and selectivity for CO₂/N₂ and CO₂/H₂ as 104 and 52, respectively. The TGA isotherm and XPS analysis of CS/SF/GNP membrane suggested a thermal stability of the prepared membrane that establishes its suitability for the gas permeation at different temperature.

pKa-Dependent Facilitated Transport of CO2 across Hyperthin Polyelectrolyte Multilayers

Hyperthin (ca. 20-30 nm thick) polyelectrolyte multilayers have been fabricated that are capable of facilitated transport of CO₂. These membranes were fabricated from polycations bearing pendant groups of varying basicity plus poly(sodium 4-styrenesulfonate) as a polycounterion. A strong dependency of such transport on the basicity of the pendant groups (i.e., fixed carrier sites) has been found, where pK_a values in the range of ca. 5-7 appear optimal.

TEA incorporated CS blend composite membrane for high CO2 separation performance

A novel triethanolamine–chitosan blend membrane exhibits better CO₂/N₂ separation performance and mechanical properties than pristine chitosan membrane.

Synthesis of imidazolium-crosslinked chitosan aerogel and its prospect as a dye removing adsorbent

Debus–Radziszewski imidazole synthesis was used to obtain crosslinked chitosan aerogel with very high adsorption towards anionic dye.